1. Field of the Invention
The present invention relates to an access control apparatus, an access control system, a processor, an access control method, a memory access control apparatus, a memory access control system, and a memory access control method which can control access to a memory.
2. Description of the Related Art
In a recent computer system, a multi-programming system which performs processing while switching a plurality of processes (programs, tasks, or jobs) is used to effectively utilize various resources such as a memory and a CPU in the computer system.
For this reason, data on a memory used in processing is disadvantageously stolen by another process or broken by overwriting.
Therefore, in a conventional technique, as disclosed in z/Architecture Principles of Operation (IBM; SA22-7832-00; December 2000) pp. 3-9 to 3-12, information called a storage key is stored in a memory every predetermined size (for example 4 kB). When a process accesses the memory, a system which compares a key held by the process with the storage key of the memory to be accessed to determine whether the memory is accessible or not.
However, in the above memory protecting system using a storage key, in addition to a memory in which data is to be stored, a memory to store a storage key is required. For this reason, an amount of hardware increases.
A protection unit is a page unit of, e.g., 4 kB. When a user intends to protect small-size data, an unused wasteful memory area is generated. This problem can be solved such that storage keys are associated with smaller memory area units. However, in this case, a larger number of memories are requested to store the storage keys.
Furthermore, when a fault occurs in the memory, the memory can be accessible, and data may be illegally read.